I've beeen doing group fitness. Started with water aerobics, tried some yoga (too hard on the hand/wrist for me; carpal tunnel), and then added spin classes. I hate spinning class sometimes, but I know that it is a good work out. After that class I feel warmth all over my body while driving home.
As far as stalls my worst has been about 2 weeks so far. I do some strength training already in the pool and I have the biceps and triceps to show for it, so if you have that available at your gym you might give it a try.
I did a fit test with a trainer this week. He said I'm in good shape (better than average) and that I just need to lose more weight.
I told him that I don't have the money to use a personal trainer and he was very understanding. The fit test was a free part of my membership. He said that the one thing that he thought would be a good investment for me on my weight loss journey is their CardioPoint test. From what I can tell they put you on a bike, or a treadmill, with a mask on and measure everything. He said that if I do that I will know what heart rate I need to target to burn fat as it varies from person to person. Then I can use a heart rate monitor to get to and stay at that rate. It would be a one time investment vs. paying a trainer all the time. I'm thinking about it.